iio:adf4350: Fix typo

There is a typo in the adf4350 driver turning a shift into a compare. This patch
fixes it.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>